l i I

1

Hydrobiologia 175: 237-256, 1989 © 1989 Kluwer Academic Publishers. Printed in Belgium 237

On the morphology and karyology of the genus Archilopsis (Meixner) (Platyhelminthes, Proseriata)

Paul M. Martens 1, Marco C. Curini-GallettF & Ileana PuccinellP 1Research group Zoology, Department SBM, Limburgs Universitair Centrum, Diepenbeek, Belgium; 2Dipartimento di Scienze dell'Ambiente e del Territorio, Universita di Pisa, Pisa, Italy; 3 Istituto di Zoologia ed Anatomia Comparata, Universita di Pisa, Pisa, Italy

Received 7 October 1987; in revised form 20 January 1988; accepted 10 March 1988

Key words: Platyhelminthes, Proseriata, Archilopsis, karyology, phylogeny

Abstract

Two new Archilopsis species are described: Archilopsis marifuga sp.n. and Archilopsis arenaria sp.n.; Archilopsis unipunctata (Fabricius, 1826) andArchilopsis spinosa (Jensen, 1878) are redescribed. The latter taxon is re-established. The descriptions are based on morphological and karyological data. The four species of the genus can unequivocally be recognized by the morphology of the cirrus and the presence or absence of a stylet. The genus Archilopsis is regarded as a monophyletic group with at least two autapomorphies. The relationship between the four species is discussed and a cladogram for the genus proposed. The existence of two sistertaxa (each with two species) is recognized.

Introduction

Fabricius (1826) described Planaria unipunctata on very superficial characteristics (according to our present criteria).It was redescribed and trans­ferred to the genus Monocelis by Oersted (1844). Claparede (1861) described specimens (as M. unipunctata) which deviate from the descrip­tions of Fabricius and Oersted, while J ens en (1878) described anew species, M. spinosa, on the basis of some features not present in the descrip­tions of M. unipunctata. Nonetheless, this species was synonymized with M. unipunctata by von Graff (as Automolus unipunctata in 1882, as M. unipunctata in 1913), while Maristo (1938) on the other hand regarded only M. spinosa J ensen, 1878 as a valid species. Finally, Meixner (1938) introduced the new genus-name Archilopsis with

the single species A. unipunctata (F abricius, 1826) (see also Ax, 1951). Two more descriptions must be taken into consideration: Luther (1960) and Karling (1974: photograph on p. 95 of which the material was available for our study).

While studying the Turbellaria on the Belgian, Dutch and Northern French coasts we found two species which both fitted the descriptions of A. unipunctata. A careful morphological (on light­and electronmicroscopic level) and a karyological analysis confrrmed that two different species were involved indeed. In the neighbourhood of the Huntsman Marine Laboratory (St. Andrews, Passamaquody Bay, Canada) we found a third species, different from the former two but still fitting the descriptions of A. unipunctata. Finally we received from Dr. B. Sopott and Dr U. Noldt (Gottingen) slides of specimens labeled A. uni-

238

Table I. Sampling places, period, collectors and collected material of the populations studied by the Authors.

Locality

Archilopsis unipunctata Iceland:

Eyjafjordur Sweden:

SOderby Vetterso Gain an Gullmmaren Kristieneberg Kristieneberg Kristieneberg

Finland: Hagno

Germany: Sylt

Canada: Passamaquoddy bay (St. Qndrews)

Archilopsis arenaria Belgium:

De Panne De panne

Oostende Zwin (beach) Heist Zwin (beach)

Germany: Sylt

France: Roscoff

Archilopsis marifuga Belgium:

Zwin (lagoon) Zwin (lagoon)

Netherlands: Texel

France: Ambleteuse (estuary of the Slack)

Canada: Passamaquoddy bay (St. Andrews)

Archilopsis spinosa England:

Plymouth Germany:

Sylt Sylt

France: Roscoff

Period

July 1947

June 1940 July 1940 July 1940

June 1969 July 1985 July 1986

March 1940

Febr. 1984

August 1984

Aug. 1981 May 1983

May 1983 May 1983 Oct.-Febr. 1983/84 Jan., March 1984

Sept. 1985

July 1986

May 1983 Sept.-Apr. 1983/84

June 1982

May 1979

May 1984

August 1984

June 1985 Sept. 1985

July 1986

Collector

Westblad

Bock Bock Bock Karling Schockaert Schockaert Schockaert

Karling

Noldt

the authors

the authors the authors

the authors the authors Jouk Re vis

the authors

the authors

the authors Re vis

the authors

E. Martens

the authors

the authors

Caps tick

Noldt the authors

the authors

Material

1 specimen serially sectioned

2 specimens serially sectioned 2 specimens serially sectioned I specimen serially sectioned I whole mount 1 whole mount 4 whole mounts 5 whole mounts 5 specimens for karyology

1 specimen serially sectioned

2 whole mounts

1 specimen semi-thin sectioned I specimen for karyology 4 whole mounts

I specimen serially sectioned 3 specimens for karyology 1 specimen semi-thin sectioned 4 specimens for karyology I 0 specimens for karyology 10 whole mounts 10 whole mounts

10 specimens for karyology 15 whole mounts

6 specimens for karyology

4 specimens for karyology 3 whole mounts

1 whole mount

2 specimens semi-thin sectioned I 0 specimens serially sectioned 4 whole mounts 2 specimens for karyology

2 whole mounts 2 specimens for karyology

2 specimens serially sectioned

3 whole mounts 2 specimens serially sectioned I specimen semi-thin sectioned 9 whole mounts 9 specimens for karyology

6 specimens for karyology

punctata collected at Sylt (Germany). These specimens appeared to be different from the three other species we had studied so far.

It has thus become clear that Archilopsis uni­punctata (Fabricius, 1826) actually consists of a complex of at least four species. Those species are here described and for two of them a new taxon is proposed.

Material and methods

Of the four species involved as many specimens as possible from various localities have been studied alive, in whole mount, in sectioned mate­rial and from a karyological point of view (Table 1). The Archilopsis material of the Swedish Museum of Natural History has been reviewed. Of two species also E. M. data are available and elsewhere presented (E. Martens & Schockaert, 1981 and E. Martens, 1986, see discussion). Animals were extracted from the sand with the MgC12 decantation technique (see P. Martens 1984a). Specimens studied alive were preserved as whole mounts with lactophemol or polyvinyl­lactophenol. Specimens for paraffin sectioning were fixed with Bouin's fluid, sectioned at 5 J.Lm and stained with iron hematoxyline - eosine. Mallory's, or Masson's triplestain. Some speci­mens were fixed with 2% glutaraldehyde, post­fixed with 2% Os04 (in cacodylate or phosphate buffer) and upon embedded, serially sectioned (with Reichert Ultracut) in 1 J.Lm sections (semi­thin) (alternating with ultra-thin sections).

Figures without a scale are freehand drawings, those with scale were made with the camera lucida. Photographs of the extremely squeezed animals for cirrus and stylet comparisons are all reproduced at the same magnification. Relative pore indices are given according to Karling (1966).

Animals used for karyological study remained alive in 0.2% colchicine for 3-4 hours, than trans­ferred in 2% acetic acid (2 min.) stained in lactic­aceto-orcein and squashed under a coverslip. These preparations have also been used for the study of the morphology of the cirrus (Papi, 1951).

239

The male germinal line was used for karyologi­cal purposes. The haploid chromosome number was ascertained from primary and secondary spermatocytes and the diploid number from spermatogonial mitoses.

Relative lengths (r.l. = length of chromosome x lOO/total length of haploid genome) and cen­tromeric indices ( c.l. = length of the short arm x lOO/length of the entire chromosome) were obtained from measurements of ten metaphase plates in each population, but the karyotype mor­phology was confirmed by a higher number of plates from different specimens. We have not con­sidered it relevant to report the c.l. values of the acrocentric chromosomes in the four species, as they showed some variations in the different plates, due to the different degree of coiling of the long arm. The short arm can be considered of almost equal length in the various pairs of the set. The idiograms of the four species are based on the mean values of all populations examined. The chromosome nomenclature employed is that of Levan et al. (1964).

Type and voucher material is deposited in the zoological collection of the department SBM, Limburgs Universitair Centrum, Diepenbeek, Belgium.

Descriptions

A. Morphology (Figs. 1-8) The habitus oftheArchilopsis species is that ofthe majority of the Monocelididae: slender and elon­gated, 3-4 mm in A. unipunctata and A. spinosa, 2-3 mm in A. marifuga and A. arenaria. They are without eyes or pigment. The gut may be light­green to yellowish depending on its content. The anterior tip is slightly narrowing and rounded, with 'olly' droplets in front of that statocyst. The posterior end is rounded and with numerous adhesive papillae.

The epidermis in all species is of the in sunk type and ciliated over the whole body, only the tail region is bared. Cilia are 2-3 J.Lm in A. unipunctata and A. arenaria, 4-5 J.Lm in A. marifuga and A. spinosa. No rhabdite-like inclusions were

240

Fig. 1. Archilopsis unipunctata: A. Habitus. B. Copulatory organs (from living animal; stylet not visible). C and D. Cirrus with stylet (from squeezed animals). E. Reconstruction of the genital organs from serial sections (seen from the right).

241

Fig. 2. Archilopsis unipunctata: photographs of the cirrus from different populations. A. Section through the cirrus with stylet (specimen from Eyjafji:irdur, Iceland). B and E. From Kristinenberg (Sweden). C and D. Sylt (Germany). G. Gullmmaren (Sweden). F. St. Andrews (Canada). H. Vetterso (Sweden). I. Galnan (Sweden). A,G-I from the collection of the Swedish

Museum of Natural History).

242

B A

.· o-'---sta

C,D

Fig. 3. Archilopsis arenaria: A. Habitus. B. Copulatory organs (from living animal). C and D. Cirrus with stylet (from squeezed animals). E. Reconstruction of the genital organs, from serial sections (seen from the left).

observed within the epidermis. In addition to the adhesive organs three kinds of glands (or glandu­lar organs) associated with the epidermis can be found in sectioned material: (1) numerous small elongated sack-like glands with a fine

eosinophilous secretion in the anterior body part (very small in A. arenaria), (2) a group of eosinophilous glands (gg2 ) behind the female pore ('kittdrusenkomplex' (Ax, 1959a)) and (3) brown to yellowish stained ovoid vesicles with a flat

243

Fig. 4. Archilopsis arenaria: Photographs of the cirrus all from the Belgian coast (A from living animal: B-D from squeezed animals).

nucleated epithelium ('rhammites': Hyman (1951) or 'rhamniten': Maristo (1938) and 'gg1':

P. Martens (1983)). In living animals this latter type of glands can be seen as bundles of long fine rods, very obvious in A. unipunctata and A. spinosa.

The pharynx lies in the second half of the body. As in most Monocelididae it is tubiform, in hori­zontal position, and orientated backwards, with longitudinal muscles at the epithelial side, circular muscles at the parenchyma side, external and internal epithelium with insunk nuclei and ciliated over the whole length; only the very distal tip of the pharynx is devoid of cilia. A distinct oeso­phageal part is missing.

Male genital organs. The number of testes varies within the species: 32-36 in A. spinosa, 24-36 in A. arenaria, 26-30 in A. unipunctata and 20-26 in A. marifuga.

The copulatory organ in the four species is basi­cally of the same construction. A detailed descrip­tion can be found in E. Martens & Schockaert (1981) incl. E.M. data (this description is actually

based on A. marifuga and not on A. unipunctata (see discussion below). The presence of the two prostate ducts could be confirmed in all four species on the lightmicroscopic level. A central stylet within the cirrus is found in A. unipunctata and A. arenaria. This stylet is to be considered a part of the ejaculatory duct (papilla), permanently everted into the cirrus. without an external epithelium, but with a thickened basement mem­brane (see also E. Martens, 1986).

In A. unipunctata (Figs. 1B and E) the bulb has a total length of 150 J..lm while the cirrus is about 75 J..lm long. The cirrus gradually widens from its proximal to its distal end. Distally it is provided with a girdle of large spines, 18-22 J..lm long (up to 25 J..lm, see Luther, 1960), while the proximal spines are 5-7 J..lm. These proximal spines are more or less triangular in shape with a rounded tip. Most of the large distal spines are broad at the basis, narrow abruptly and end into slender elon­gated tips, rounded at the edge. Among these distal spines 2 or 3 are slightly larger than the other ones and do not have the abrupt narrowing. In the proximal half of the (inverted) cirrus a large

244

Fig. 5. Archilopsis marifuga: A. Habitus. B. Copulatory organs from living animal. C and D. Cirrus (from squezed animals). E. Reconstruction of the genital organs, from serial sections (seen from the right).

central stylet like structure is present, 40-45 J.lm long and 27-30 J.lm broad. It is clearly visible in well squeezed animals, especially when the stylet protrudes from the exerted cirrus (Figs. lC-D and 2). In sectioned material the stylet becomes

apparent as a prolongation of the ejaculatory duct which penetrates the cirrus. The epithelium above the thickened basale lamina has been lost. This structures not visible in living or poorly squeezed animals (Figs. lA-B) can easily be overlooked in

245

Fig. 6. Archilopsis marifuga: Photographs of the cirrus from different populations. A and B Texel (Netherlands) C. St. Andrews (Canada) D. Ambleteuse (France) E and F. Zwin (Belgium) (A, B from living animals; C-F from squeezed animals).

sectioned material because the stylet wall is laying close to the spines of the cirrus. The part of the ejaculatory duct between the stylet and the prostate ducts is short.

In A. arenaria (Figs. 3B and E) the copulatory bulb has a total length of about 100 Jlm, the cirrus is about 40 Jlm long with a stylet within its proxi­mal part (27-37 Jlm long and 10-13 Jlm broad). The proximal 2/3 of the cirrus is a straight tube (due to the presence of the stylet) and narrows in its distal part (Figs. 3AB, 4A and B). The spines are rather uniform and triangular, the distal spines being slightly larger than the proximal ones (7 Jlm to 4 Jlm). Here the ejaculatory duct between the stylet and the prostate ducts is also rather short.

In A. marifuga (Figs. 5B and E. 6) the copula­tory bulb has a total length of 150 Jlm and the cirrus is about 50-55 Jlm long. No inner stylet is present. The proximal part of the cirrus is slightly broadened and is followed by a constriction from where the cirrus again widens distally. The spines of the cirrus are uniform in shape, narrow con­tinuously and are sharply pointed. The distal spines are slightly longer than the proximal ones (from 14-12 Jlm to 7 Jlm). In squeezed animals it can be seen that the spines of the proximal part of the cirrus are slightly isolated from the others. The ejaculatory duct does not penetrate the cirrus and is much longer than in the former species. In A. spinosa (Figs. 7B and E, 8) the copulatory

246

B

\ \ . \ I

' I ' I '

\ I

\ \

\ \

\ \ \A~,\ \~t\ \ /)11 \ ~\ \~)

E

Fig. 7. Archilopsis spinosa: A. Habitus. B. Copulatory organs from living animal. C and D. Cirrus (from squeezed animals). E. Reconstruction of the genital organs, from semi-thin sections (seen from the left).

247

Fig. 8. Archilopsis spinosa: Photographs of the cirrus from the Sylt population (Germany), from squeezed animals.

bulb is about 180 f.-liD long and the cirrus about 90 f.-liD. The cirrus gradually broadens from proxi­mal to distal, while the spines become larger (from 3-4 f.-liD up to 17-20 f.-liD). In the most distal part of the ejaculatory duct an isolated row of 9-13 very small spines occurs at one side of the lumen (cfr. Jensen 1878, p. 70, Fig. 7c). All spines have the same shape, broad at the basis and gradually narrowing to the pointed tip. The ejaculatory duct is extremely long (about 230 f.-liD including the section with the small spines) in this species.

Female genital organs. (Fig. lE, 3E, 5E, 7E). The ovaries are situated ventro-laterally in front of the pharynx. The vitellaria are dorso-laterally stretched from about halfway the row of testes to the level of the copulatory bulb. The ovovitel­loducts fuse behind the pharynx to form the corn-

m on female duct which has a high nucleated and non-called epithelium. This duct then runs to the female pore. In front of the copulatory bulb the duct widens, forming a bursa of the resorbiens type with a strongly vacuolated epithelium. In all four species a vagina internal starting in the male atrium is present. It continues as a 'vaginal duct' over the copulatory bulb to the female ( oviposi­tory) pore where it is joined by the common female duct. This pore is surrounded by female glands. The epithelium of the vagina is high, not ciliated, with insunk nuclei and strongly eosinophilous (secretory epithelium?). The vaginal duct is lined with a ciliated epithelium with in sunk nuclei. Both vagina and vaginal duct are surrounded by a well developed muscular layer. A postpenial bursa with an epithelium of the resorbiens type opens into the vaginal duct above the copulatory bulb.

248

Table 2. Biometrical data of some species characteristics of the Archilopsis species.

A. marifuga

Length of animals

A. spinosa

3-4mm ± 180 Jlm

A. arenaria A. unipunctata

Length of the copularoty bulb Length of the cirrus

2-3 mm ± 150 Jlm

± 55 Jlm ± 90 Jlm (distal part)

2.5-3 mm ± 100 Jlm ± 40 Jlm

3-4mm ± 150 Jlm

± 75 Jlm Stylet:

-length -breadth

Length of the cirrus spines: - proximal spines - distal spines

Number of specimens used for measurements

7Jlm 12-14 Jlm

10

3-4 Jlm 17-20 Jlm

12

Its epithelium is connected with the gastrodermis and in some places there is only a thin layer of tissue between the gut lumen and the bursa lumen (in A. marifuga this bursa lies more to the anterior, the bursal tissue being stretched over the vaginal duct nearly as far as the posterior end of the copulatory bulbus; this situation is probably the result of contraction (Fig. SE))

B. Karyology All four species show the same diploid number 2n = 10 (Fig. 9). The diploid chromosome complement is formed by 5 parts of homologous chromosomes gradually decreasing in length, the shortest chromosome being approximately 2/3 of the longest one. All four species have almost the same total karyotype length and the correspond­ing chromosome pairs have about the same rela­tive and absolute length (Tables 3 and 4).

None of the four species showed any apprecia­ble difference among the various populations in­vestigated; in the case of both A. unipunctata and A. marifuga a remarkable homogeneity was pres­ent in the populations of the same species on either side of the Atlantic ocean.

There are no significant differences between the karyotype of A. marifuga and A. spinosa (Table 4). All chromosomes are clearly acrocen­tric with values of the centromeric index more or

27-37 Jlm 10-13 Jlm

4Jlm

7Jlm

30

40-45 Jlm

27-30 Jlm

5-7 ftm 18-22 Jlm 20-21 Jlm (Maristo, 1938) 20-25 Jlm (Luther, 1960

Fig. 29 G,H) 12

less markedly lower than 12.5 (the upper border of the acrocentric class, according to Levan et al., 1964).

In A. arenaria and A. unipunctata four chromo­somes out of five (pairs no. 1,3,4,5) are acrocentric (c.i. < 12.5), chromosome pair no. 2 is sub­metacentric in both species ( c.i. 34.22 in A. arenaria and 36.19 in A. unipunctata see Table 3). With this value the second chromosome of A. unipunctata lies close to the border between metacentric and submetacentric (classification according to Levan et al., 1964). These differences between A. arenaria and A. unipunctata are not significant.

For all the species the haploid number n = 5 was ascertained in spermatocytes I and 11. The chiasma frequency observed in spermatocytes I is low, in accordance with was already reported for other Monocelididae (Curini-Galletti et al., 1984; Curini-Galletti et al., 1985).

Diagnosis and occurrence of the Archilopsis -species

Archilopsis Meixner, 1938: Monocelididae with pharynx in the posterior body half, ovaries in front of the pharynx. Copulatory organ of the type with spiny cirrus with or without a central stylet.

A. marifuga 249 10-

0

10- ·~)~., 20-

~ - _, 30-

A. spinosa -

''"'"~~ ··~.

"' 1/

- .){\~ - ~~~'SI - tJ'tt A. arenaria

-

S( - ~ ,, - ~~~

'l~r A. unipunctata

-

Ill

~+ -?~~

- ~V ~~- IJ

10 11-m ,_" . Fig. 9. ldiograms, plates and drawing of the karyotypes from spermatogonial mitosis.

250

Table 3. Karyometric data from the five chromosomes of the haploid set of Archilopsis unipunctata and Archilopsis arenaria.

Population Chromosome

2

Archilopsis unipunctata Passamaquoddy r.l.: 24.07 ± 1.71 21.86 ± 2.16 bay (Canada) c.i.: ~ 12.5 37.50 ± 2.26

size (J.tm) 3.13 ± 0.42 2.82 ± 0.24 nomencl.: t mjsm

Kristieneberg r.l.: 23.19 ± 0.77 21.25 ± 1.92 (Sweden) c.i.: ~ 12.5 34.88 ± 2.22

size (J.tm) 3.26 ± 0.36 3.00 ± 0.51 nomencl.: t sm

means r.l.: 23.63 21.55 c.i.: ~ 12.5 36.19 size (J.tm) 3.19 2.91 nomencl.: sm

Archilopsis arenaria De panne r.l.: 24.52 ± 1.80 21.19 ± 1.09 (Belgium) c.i.: ~ 12.5 33.56 ± 3.07

size (J.tm) 3.08 ± 0.21 2.67 ± 0.26 nomencl.: t sm

Oostende r.l.: 23.03 ± 1.05 22.52 ± 0.49 (Belgium) c.i.: ~ 12.5 35.14 ± 2.50

size (J.tm) 3.21 ± 0.41 3.11 ± 0.47 nomencl.: t sm

Zwin r.l.: 23.12 ± 1.47 21.19 ± 1.25 (Belgium) c.i.: ~ 12.5 33.27 ± 2.43

size (J.tm) 2.63 ± 0.33 2.43 ± 0.28 nomencl.: t sm

Sylt r.l.: 23.02 ± 1.03 21.04 ± 1.03 (Germany) c.i.: ~ 12.5 35.19 ± 3.30

size (J.tm) 2.55 ± 0.38 2.33 ± 0.37 nomencl.: t sm

Roscoff r.l.: 22.39 ± 1.08 21.90 ± 2.13 (France) c.i.: ~ 12.5 33.96 ± 3.22

size (J.tm) 2.58 ± 0.33 2.47 ± 0.39 nomencl.: t sm

means r.l.: 23.22 21.57 c.i.: ~ 12.5 34.22 size (J.tm) 2.81 2.60 nomencl.: sm

Prostate glands discharge in the ejaculatory duct via two prostate ducts. Internal vagina prepenial associated with the male atrium. Vagina con­nected with the common females duct behind the copulatory bulb by a vaginal duct with a (post­penial) bursa. Karyotype: five pairs of homolo-

Haploid karyotype length (J.tm)

3 4 5

20.69 ± 1.32 17.98 ± 1.14 15.39 ± 1.06 ~ 12.5 ~12.5 ~ 12.5 13.02 ± 0.92 2.68 ± 0.28 2.38 ± 0.25 2.01 ± 0.14

t t t 20.37 ± 0.94 18.87 ± 0.77 16.32 ± 0.63 ~12.5 ~ 12.5 ~ 12.5 14.09 ± 1.74 2.86 ± 0.37 2.65 ± 0.33 2.30 ± 0.31

t t t 20.53 18.42 15.85 ~12.5 ~12.5 ~12.5 13.55 2.77 2.51 2.15

20.90 ± 1.06 17.99 ± 0.79 15.39 ± 1.17 ~12.5 ~ 12.5 ~ 12.5 12.59 ± 0.63 2.63 ± 0.21 2.27 ± 0.27 1.94 ± 0.26

t t t 21.25 ± 0.53 17.90 ± 1.40 15.35 ± 0.41 ~12.5 ~12.5 ~12.5 13.97 ± 2.02 2.97 ± 0.38 2.25 ± 0.49 2.16 ± 0.33

t t t 20.38 ± 0.49 18.85 ± 1.14 16.60 ± 1.49 ~12.5 ~12.5 ~12.5 11.34 ± 0.95 2.34 ± 0.20 2.10 ± 0.20 1.84 ± 0.17

t t t 20.5 ± 0.46 18.8 ± 0.57 16.63 ± 0.86 ~ 12.5 ~ 12.5 ~ 12.5 11.09 ± 1.77 2.28 ± 0.39 1.99 ± 0.55 1.84 ± 0.31

t t t 20.42 ± 0.95 18.67 ± 0.90 16.54 ± 1.01 ~12.5 ~ 12.5 ~ 12.5 11.24 ± 1.26 2.30 ± 0.25 2.10 ± 0.25 1.85 ± 0.19

t t t 20.69 18.44 16 .10 ~12.5 ~ 12.5 ~ 12.5 12.05 2.50 2.14 1.93

gous chromosomes gradually decreasing in length. Four out of five pairs are acrocentric, the second pair being submetacentric or acrocentric.

Archilopsis unipunctata (Fabricius, 1826): Cirrus about 75 J.lm long, continuously widening from

251

Table 4. Karyometric data from the five chromosomes of the haploid set of Archilopsis marifuga and Archilopsis spinosa.

Population Chromosome

2

Archilopsis marifuga Zwin r.l.: 25.58 ± 1.65 22.03 ± 0.70 (Belgium) c.i.: ;£ 12.5 ;£ 12.5

size (J.Lm) 3.35 ± 0.64 2.83 ± 0.56 nomencl.: t t

Ambleteuse r.l.: 23.96 ± 1.09 21.23 ± 0.38 (France) c.i.: ;£ 12.5 ;£ 12.5

size (J.Lm) 3.33 ± 0.09 2.95 ± 0.99 nomencl.: t t

Passamaquoddy r.l.: 23.95 ± 1.04 21.56 ± 0.54 Bay (Canada) c.i.: ;£ 12.5 ;£ 12.5

size (J.Lm) 2.93 ± 0.14 2.63 ± 0.10 nomencl.: t t

means r.l.: 24.49 21.61 c.i.: ;£ 12.5 ;£ 12.5 size (J.Lm) 3.20 2.82 nomencl.: t

Archilopsis spinosa Sylt r.l.: 23.05 ± 0.99 21.49 ± 0.70 (Germany) c.i.: ;£ 12.5 ;£ 12.5

size (J.Lm) 3.14 ± 0.25 2.93 ± 0.26 nomencl.: t t

Roscoff r.l.: 22.88 ± 0.80 21.37 ± 0.77 (France) c.i.: ;£ 12.5 ;£ 12.5

size (J.Lm) 3.15 ± 0.66 2.94 ± 0.60 nomencl.: t t

means r.l.: 22.96 21.43 c.i.: ;£ 12.5 ;£ 12.5 size (J.Lm) 3.14 2.93 nomencl.: t

proximal to distal end. Distally with a girdle of large spines (18-25 f.lm long), proximal spines much shorter (5-7 f.lm). Spines mostly rounded at the "tip. Stylet (only visible in well squeezed animals or sectioned animals); 40-45 f.lm long and 27-30 f.lm broad. Pore indices: 4-2-6.

Karyotype: 4 pairs of acrocentric chromo­somes, and one pair submetacentric (the second).

Occurrence: A long list of localities for this species is given by Luther (1960). The identifi­cation of the species is, however, doubtful in numerous cases (see discussion below) and only findings after 1938 (description of Meixner and Maristo) may be unambiguously accepted. From

Haploid karyotype length (J.Lm)

3 4 5

19.58 ± 0.93 17.47 ± 0.88 15.39 ± 1.00 ;£ 12.5 ;£ 12.5 ;£ 12.5 13.21 ± 2.39 2.61 ± 0.48 2.34 ± 0.45 2.08 ± 0.47

t t t 20.28 ± 0.83 18.43 ± 0.49 16.09 ± 1.57 ;£ 12.5 ;£ 12.5 ;£ 12.5 13.91 ± 3.56 2.80 ± 0.62 2.56 ± 0.62 2.27 ± 0.47

t t t 19.65 ± 0.86 18.37 ± 0.76 16.49 ± 0.68 ;£ 12.5 ;£ 12.5 ;£ 12.5 12.24 ± 0.43 2.40 ± 0.12 2.26 ± 0.15 2.02 ± 0.12

t t t 19.84 18.09 15.99 ;£ 12.5 ;£ 12.5 ;£ 12.5 13.12 2.60 2.39 2.12

20.23 ± 0.46 18.62 ± 0.61 16.61 ± 1.04 ;£ 12.5 ;£ 12.5 ;£ 12.5 13.63 ± 1.28 2.76 ± 0.27 2.54 ± 0.26 2.27 ± 0.30

t t t 20.18 ± 0.58 18.47 ± 0.91 17.10 ± 1.07 ;£ 12.5 ;£ 12.5 ;£ 12.5 13.73 ± 2.51 2.77 ± 0.49 2.53 ± 0.40 2.34 ± 0.42

t t t 20.20 18.54 16.85 ;£ 12.5 ;£ 12.5 ;£ 12.5 13.68 2.76 2.53 2.30

these findings it can be concluded that A. uni­punctata has a North-Atlantic and Baltic (Karling, 1974) distribution and never occurs on open beaches with high dynamic. A. unipunctata is most probably absent in the Mediterranean since it has never been found there after 1938. A. unipunctata is a eurytope and euryhaline species, found on macrophytes and higher plants, in sand varying from coarse sand with gravel to fine sand with silt and detritus in places which are more or less protected (lagoones, estuaries, closed seas etc.). Archilopsis arenaria sp.n.: Cirrus about 40 f.lm long, with stylet about 10-13 f.lm broad and

252

27-37 JLm long. Cirrus narrows from proximal to distal. Spines of the cirrus almost uniform, triangular, the distal spines longer (7 JLm) than the proximal ones (4 JLm). Pore indices 3-2-8.

Karyotype: 4 pairs of acrocentric chromo­somes, one pair submetacentric (the second). Occurrence: This species has been found in fine to medium sand in the mediolitoral of beaches along the Belgian coast, near the littoral station of Sylt and in front of the Biological Station of Roscoff, in exposed and in protected but genuinely marine localities (Table 1). This species is recently mentioned by Ax & Armonies (1987) for the Canadian east coast.

Type locality: Belgium North-Sea coast, De Panne, mediolittoral, fine sand, August 1981.

Holotype: One whole mount (paratype: one specimen serially sectioned, Heidenhain's hemo­toxyline-eosine ).

N .B. : This species has been reported as Archilopsis unipunctata by P. Martens (1984a) and as Archilopsis sp. by E. Martens (1986).

Archilopsis marifuga sp.n.: Cirrus about 50-55 JLm long with a constriction in the proximal third, without a stylet. Distal spines larger (12-14 JLm) then the proximal ones (about 7 JLm). Ejaculatory duct long without isolated spines nor forming a stylet within the cirrus. Pore indices: 4-2-6.

Karyotype: 5 pairs of acrocentric chromosomes. Occurrence: This species was found in rather

fme sand with silt and detritus, always in a more or less protected area, generally in brackish water. For known localities see Table 1.

Type locality: estuary of the Slack, Ambleteuse (France), fme sand with mud, May 1979.

Holotype: One whole mount (paratype: dif­ferent specimens serially sectioned, Masson's Triplestain ).

N.B.: This species has been reported as Archilopsis unipunctata by Martens and Scho­ckaert (1981).

Archilopsis spinosa (Jensen, 1878): Cirrus large, about 90 JLm long without a stylet, gradually nar­rowing from distal to the proximal. Distal spines

about 17-20 JLm long. Halfway in the long ejacu­latory duct there is a row of isolated small spines. Pore indices: 4-2-5.

Karyotype: 5 pairs of acrocentric chromo­somes.

Occurrence: This species was found by us in sand with silt and detritus on sandflats in marine localities. Due to possible confusion with the other species, it is known with certainty only from type locality (Herlo, Norway, on Fucus: Jensen 1878) and from localities reported in Table 1. The reports of Ax (1951) and Sopott (1972) are proba­bly referred to this species. This species is also recently mentioned by Ax & Armonies (1987) for the Canadian east coast but under the provisional name A. inopinata.

Discussion

A. Taxonomy From the descriptions it is clear that four different species can be discerned within the genus Archilopsis. They differ in a number of morpho­logical characteristics: size shape and distribution of cirrus-spines, presence or absence of a stylet within the cirrus (some biometrical data are pre­sented and compared in Table 2), and in their karyology (Tables 3 and 4).

Which of these four species is to be regarded as A. unipunctata (Fabricius, 1826)? Of all known descriptions, those of Maristo (1938), Luther (1960) and Karling (1974) deal with the same species under different names. Non of them exactly mentions the presence of a stylet but this can easily be overlooked. On the other hand the drawings of Luther (1960 Fig. 29 G,I and J) all show an everted cirrus with at the top a well lined penis papilla which might be a weakly developed hard structure. On Karling's photograph (1974 Fig 176) it is possible to recognize the stylet (see Fig. 2G). Also Meixner (in his second and unpub­lished part of 'Die Tierwelt der Nord- und Ostsee') draws a straight tube at the top of the exerted cirrus.

From these interpretations as well as from our

observations (including the material from the Swedisch Museum) it must be pointed out that A. unipunctata has a stylet within the cirrus which can be protruded by everting the cirrus. This obviously weakly developed hard structure has the same basic constriction as the stylet of other Monocelididae (own observations).

Jensen (1878) described Monocelis spinosa as characterized by an extremely long ejaculatory duct provided with some isolated small spines. Three of the populations we have studied perfectly fit Jensen's description, so that we consider the taxon Archilopsis spinosa (Jensen, 1878) as valid.

No taxa are available for the other two species, and we need to consider them as new: Archilopsis arenaria sp.n. and Archilopsis marifuga sp.n.

'Archilopsis unipunctata' described by E. Martens & Schockaert (1981) does not present a stylet. We have investigated the same material as well as living animals from the same locality (see Table 1). They are here reported as A. marifuga.

In a preliminary revision of the Monocelididae, Karling (1966) has proposed to lump together a number of genera - among which Archilopsis -into the genus Archiloa de Beauchamp, 1910 mainly based on the presence of a copulatory organ of the conjuncta-duplex type with a spiny cirrus. From our present knowledge of a number of the genera concerned (own unpublished data) and from the underlaying descriptions, we suggest to maintain the genus Archilopsis Meixner, 1938 as a valid genus name. At least two synapomorphies can be indicated for the four species concerned: ( 1) the prostate glands which discharge into a pair of prostate ducts (see also E. Martens & Schockaert, 1981) and (2) the vagina interna con­tinues in a long vaginal duct which is connected postpenially with a bursa and the female duct.

B. Relationships From a morphological point of view the four Archilopsis species can be grouped two by two: A. unipunctata and A. arenaria on the one hand and A. marifuga and A. spinosa on the other hand. The first pair of species has a stylet within the cirrus, formed by a stabilized protrusion of the ejaculatory duct covered by a basal lamina deriva-

253

tion at its outer side (see E. Martens, 1986 for A. arenaria). A stylet of a similar origin is found in some Duplominona species (Ax & Ax 1977; P. Martens, 1984b) and in Archilina endostyla (Ax, 1959b ). The presence of such a stylet is clearly an apomorphy, probably a parallelism in species not closely related, but it may be a synapomorphy within the genus Archilopsis (see also below).

The second pair of species, A. marifuga and A. spinosa, has some small proximal spines more or less separated from the other spines. In A. marifuga (see Fig. 5B) they lay less separated in the proximal part of the cirrus, while these clearly form an isolated group within the ejacula­tory duct in A. spinosa. This characteristic is an apomorphy, maybe a synapomorphy for these two species (from outgroup comparison).

All four Archilopsis species have a chromosome set of 2n = 10 with almost the same absolute karyotype length and relative chromosome lengths. Chromosomes 1,3,4,5 are acrocentric ( c.i. < 12.5) in all species. Chromosome 2 is acro­centric in A. marifuga and in A. spinosa while the c.i. = 34.22 in A. arenaria and c.i. = 36.13 in A. unipunctata (these c.i. are not significantly dif­ferent: p > 0.05). Since relative length of this second chromosome is the same in the four species, a pericentric inversion must underlie the differences in centromeric position. From a com­pariSOJ?. with the karyotypes of other Mono­celididae (Curini-Galletti et al., 1985; Curini­Galletti et al., 1988) it can be concluded that the set with 5 acrocentric chromosomes is the plesio­morph situation, and a submetacentric second chromosome due to pericentric inversion is an apomorphy, probably a synapomorphy for A. arenaria and A. unipunctata, which is congruent with the presence of the stylet within the cirrus.

The genus Archilopsis can thus be regarded as being composed of two sister-taxa, each of which consists oftwo sister-species (Fig. 10). Curiously enough, in each pair of species we fmd one (A. unipunctata and A. marifuga) in less dynamic habitats (even brackish water) and one (A. arena­ria and A. spinosa respectively) in true marine habitat with higher dynamics. Apparently each

254

----------- Archilopsis ---------~

A. marifuga

prox. spines

D plesiomorphy

• apomorphy

A. spinosa A. arenarta A. unipunctata

inversion

vaginal duct (with bursa)

prostatic ducts

acrocentric chromosomes

no spines isolated

Fig. 10. Phylogenetic relationship within the genus Archilopsis.

species seems to be ecologically isolated from its sister-species while the two pairs of sister-species are clearly genetically separated.

With the data now available on the other Mono­celididae with a duplex copulatory organ, we find it premature to discuss the relationship of the genus Archilopsis with the other genera.

Acknowledgements

The following persons are gratefully acknowl­edged for the hospitality, research facilities and/or loaning of material: Prof. Dr. M. Burt (Canada), Prof. Dr. P. Ax, Dr. B. Sopott, Dr. U. Noldt (Gottingen, Germany), Dr. K. Reise (Sylt,

Germany), Prof. Dr. P. Lasserre (Roscoff, France), Prof. Dr. T. Karling (Sweden) and Dr. E. Martens, N. Revis and P. Jouk (Belgium).

We also wish to thank Prof. Dr. E. Schockaert for the valuable discussions and critical reading of the manuscript and Prof. Dr. T. Karling for hav­ing addressed our attention to the taxon A. spinosa (Jensen, 1878). Ms. M. Uytterhaegen is acknowl­edged for reading the English of the manuscript and Mr. and Mrs. Withofs-Ieven and Mrs. H. Zurings for the technical assistance.

Abbreviations in the figures

b bursa ci cirrus co copulatory organ ejd ejaculatory duct fd female duct fg female glands fp female pore gg glands m mouth mpmale pore ov ovary pd prostatic duct pg prostate glands ph pharynx s stylet sd seminal duct sta statocyst t testes v vagina vd vaginal duct vi vitellary vs seminal vesicle

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